Optical recording medium, and method and apparatus for reproduction

ABSTRACT

An optical recording medium having plural recording layers includes a first recording layer on which first data is to be recorded and a second recording layer on which second data is to be recorded. The first and second recording layers are layered, with the second data being recorded at a location in the second recording layer in the vicinity of a location in the first recording layer where the first data relevant to the second data is recorded. Replay signals of variable configurations can be obtained by suitably synthesizing data read out from the respective recording layers.

TECHNICAL FIELD

This invention relates to an optical recording medium and a method andapparatus for reproducing the optical recording medium. Moreparticularly, it relates to an optical recording medium having first andsecond recording layers and to a method and apparatus for reproducingthe optical recording medium.

BACKGROUND ART

As a recording medium for a variety of the information, such as audio orvideo information, an optical disc, as this recording medium, carryingthereon the recorded information, adapted to be reproduced using a lightbeam, is in widespread use. In such optical disc, it has been proposedto provide for plural recording layers in order to increase the volumeof the recordable information.

Meanwhile, in the optical disc having plural recording layers, proposedso far, data in the respective recording layers are recorded so as to besequentially reproduced from one recording layer to another. That is, inthis optical disc, data recorded on one recording layer is reproducedfirst and subsequently the data recorded on another recording layer isreproduced to reproduce the entire data recorded on each recordinglayer.

Alternatively, one of plural sectors provided on one recording layer ofthe optical disc is reproduced first, and subsequently another one ofthe sectors, provided on another one of the recording layers isreproduced.

In the multi-layered optical disc, proposed so far, the recordingcapacity of the optical disc is increased by providing plural recordinglayers. However, the data recorded on the respective recording layersare reproduced without relevance to one another. So, the data recordedon the respectively, recording layers are simply reproduced as the dataare recorded in the respective recording layers

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to provide an opticalrecording medium in which first and second reciprocally relevant data,recorded on the first and second superposed recording layers can be readout readily by a sole readout mechanism to provide diversified playbackinformation.

An optical recording medium according to the present invention has atleast a first recording layer for recording first data and a secondrecording layer for recording second data relevant to the first data.The first and second recording layers are layered together, the seconddata being recorded in a location in the second recording layer inproximity to a location in the first recording layer where the firstdata relevant to the second recording layer is recorded. So, the firstand second data, recorded on different recording layers, can be read outsequentially.

The second data is recorded within a range accessible for an objectivelens operating as readout means, adapted for reading out the first orsecond data of the first and second recording layers of the recordingmedium, by shifting the objective lens from the location of the firstrecording layer having recorded therein the first data relevant to thesecond data. So, the first and second data, relevant to each other,recorded on different recording layers, can be read out in succession.

The second data used constitutes a sole unitary recording data alongwith the first data.

A reproducing apparatus for reproducing data recorded on this opticalrecording medium according to the present invention includes readoutmeans for reading out first and second data, relevant to each other,recorded in the first and second recording layers superposed on theoptical recording medium, and reproducing means for generating playbacksignals based on the first and second data read out by this readoutmeans. A controller manages control to read out the first and seconddata recorded on the first and second recording layers and to synthesizethe first and second data to output the synthesized first and seconddata.

According to the present invention, respective data relevant to eachother, recorded in the plural layers of the optical recording medium,are read out by readout means, such as an optical pickup, provided withan objective lens, the data so generated being read out alternately andsynthesized for reproduction to provide for variegated datareproduction.

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description of thepresent invention and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an embodiment of an opticaldisc of the present invention.

FIG. 2 is a cross-sectional view showing another embodiment of anoptical disc of the present invention.

FIG. 3 is a cross-sectional view showing still another embodiment of anoptical disc of the present invention.

FIG. 4 shows a typical disposition of a loudspeaker for audio signalsrecorded on an optical disc of the present invention.

FIGS. 5A and 5B show a data structure of first and second data recordedon the first and second recording layers of the optical disc.

FIG. 6 is a schematically shows the state of recording of data on thefirst and second recording layers of the optical disc.

FIG. 7 is a block diagram showing a reproducing apparatus forreproducing an optical disc according to the present invention.

FIG. 8 is a block diagram showing a reproducing apparatus for theoptical disc according to the present invention.

FIGS. 9A and 9B show switching timing in reproducing the first andsecond data.

FIG. 10 shows another typical disposition of a loudspeaker for audiosignals recorded on an optical disc of the present invention.

FIG. 11 shows another typical data structure of first and second datarecorded on an optical disc of the present invention.

FIG. 12 shows still another typical disposition of a loudspeaker foraudio signals recorded on an optical disc of the present invention.

FIG. 13 shows still another typical data structure of first and seconddata recorded on an optical disc of the present invention.

FIG. 14 shows yet another typical data structure of first and seconddata recorded on an optical disc of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to the drawings, specified embodiments of an optical recordingmedium and a method and apparatus for reproducing the optical recordingmedium are explained in detail.

The optical recording medium according to the present invention isconstructed e.g., as an optical disc. The optical disc, to which thepresent invention is applied, is configured as shown for example inFIGS. 1 to 3.

An optical disc 1, shown in FIG. 1, includes a first recording medium 4,comprised of a first recording layer 3 formed on one surface of a firstsubstrate 2, exhibiting light transmission properties, and a secondrecording medium 7, comprised of a second recording layer 6 formed onone surface of a second substrate 5, exhibiting light transmissionproperties. The first recording medium 4 and the second recording medium6 are bonded together via a light-transmitting adhesive layer 8 with thesides thereof carrying the first and second recording layers facing eachother. The so-constructed optical disc 1 is made up of the first andsecond recording layers 3, 6 layered together via adhesive layer 8.Meanwhile, the adhesive layer 8 is of such a sufficient thickness thatneither the first recording layer 3 nor the second recording layer 6 isdisposed within the depth of focus of a light beam L which will beexplained subsequently. The layering in the context of the presentspecification denotes such a state in which the first recording layer 3and the second recording layer 6 run parallel to each other, withneither the first recording layer 3 nor the second recording layer 6being disposed within the depth of focus of the illuminating light beamL.

The first recording layer 3 of the optical disc 1 according to thepresent invention is formed as a semi-transmitting layer so that lightbeam L is illuminated onto the second recording layer 6 via the firstrecording layer 3 from the same direction as the light beam illuminatingdirection to the first recording layer 3 to reproduce data recorded onthe second recording layer 6 based on the light beam reflected back fromthe second recording layer 6.

In the present optical disc 1, switching between reproduction of datarecorded on the first recording layer 3 and that of data recorded on thesecond recording layer 6 is by changing the focal point position of thelight beam L illuminated on the optical disc 1 between the firstrecording layer 3 and the second recording layer 6.

An optical disc 1 a, shown in FIG. 2, is made up of a first recordingmedium 4 a, comprised of a first recording layer 3 a formed on onesurface of a first substrate 2 a, exhibiting light transmissioncharacteristics, and a second recording medium 7 a, comprised of asecond recording layer 6 a formed on one surface of a second substrate 5a, exhibiting light transmission characteristics. The first recordingmedium 4 a and the second recording medium 7 a are bonded together via alight-transmitting adhesive layer 8 a The optical disc 1 a shown in FIG.2 is comprised of the first and second recording mediums 4 a, 7 a bondedtogether side-by-side so that the second substrate 5 a will be locatedon the first recording layer 3 a. The first recording layer 3 a and thesecond recording layer 6 a are separated from each other by the adhesivelayer 8 a so that the layers 3 a, 6 a are not located within the depthof focus of the light beam L which will be explained subsequently.

In the above-described optical disc 1 a, data recorded on the first andsecond recording layers 3 a, 6 a are reproduced based on a light beam Lilluminated from the substrate 2 a of the first recording medium 4 a andreflected by the first recording layer 3 a and also based on a lightbeam illuminated on the second recording layer 6 a via the firstrecording layer 3 a and reflected by the second recording layer 6 a ofthe light illuminated on the second recording layer 6 a through thefirst recording layer 3 a. In this optical disc 1 a, switching betweenreproduction of data recorded on the first recording layer 3 a and thatof data recorded on the second recording layer 6 a is by changing thefocal point position of the light beam L illuminated on the optical disc1 between the first recording layer 3 a and the second recording layer 6a. An optical disc 1 b shown in FIG. 3 includes a substrate 2 b oflight-transmitting synthetic resin, such as polycarbonate resin orglass. On one surface of the substrate 2 b is formed a first recordinglayer 3 b. This first recording layer 3 b is formed as a semitransparentfilm transmitting a pre-set amount of the light beam L illuminated fromthe substrate 2 b and reflecting its pre-set amount. On the firstrecording layer 3 b is layered a second recording layer 6 b via anintermediate layer 10 formed of a light-transmitting UV light curableresin. The intermediate layer 10 is formed to a pre-set thickness sinceit performs the role of optically isolating the first recording layer 3b and the second recording layer 6 b from each other so that theselayers will not be located within the depth of focus of the objectivelens converging and illuminating the light beam L on the recordinglayers 3 b, 6 b. On the second recording layer 6 b is formed aprotective layer 9 b of, for example, UV light curable resin, forprotecting the surface of the recording layer 6 b.

In the above-described optical disc 1 b, data recorded on the first andsecond recording layers 3 b, 6 b are reproduced by detecting the lightbeam illuminated from the substrate 2 b and reflected by the firstrecording layer 3 b and also by detecting the light beam illuminated onthe second recording layer 6 b through the first recording layer 3 b andthe light beam illuminated on the second recording layer 6 b via thefirst recording layer 3 b and reflected by the second recording layer 6b. In this optical disc 1 b, switching between reproduction of datarecorded on the first recording layer 3 b and that of data recorded onthe second recording layer 6 b again is by changing the focal pointposition of the light beam L illuminated on the optical disc 1 betweenthe first recording layer 3 b and the second recording layer 6 b.

In the optical discs 1, 1 a, 1 b, according to the present invention,first data and second data, relevant to each other, are recorded on thefirst recording layers 3, 3 a, 3 b and the second recording layers 6, 6a, 6 b. The first and second data may also be multi-channel audio datasynthesized together to give unit recording data, for example,multi-channel audio data which enables surround reproduction.

The multi-channel audio data are left and right front channel data inputto left and right front speakers 11, 12 arranged ahead of an acousticspace forwardly of a listener, and left and right rear channel datainput to left and right rear speakers 13, 14 arranged in back of anacoustic space rearwardly of the listener, as shown in FIG. 4.

The left and right channel data are recorded as first data on the firstrecording layers 3, 3 a, 3 b, whilst the left and right rear channeldata are recorded as first data on the second recording layers 6, 6 a, 6b. The first data may be handled as meaningful reproduced main databecause the first data reproduced alone enable usual two-channel stereoreproduction. On the other hand, the second data may be handled assub-data relevant to the main data because it can be reproduced with thefirst data to enable so-called multi-channel audio reproduction.

It is noted that left and right front channel data Lf, Rf, recorded asthe first data on the first recording layers 3, 3 a, 3 b, are quantizedas 16-bit data for each of the left and right channel data, as shown inFIG. 5A. Moreover, left and right rear channel data Lb, Rb, recorded asthe second data on the second recording layer 6, are quantized as 16-bitdata for each of the left and right channel data, as shown in FIG. 5B.

Taking the optical disc 1, shown in FIG. 1, as an example, the seconddata recorded on the second recording layers 6, 6 a, 6 b are recorded atB1, B2, . . . locations of the second recording layer 6 in the vicinityof A1, A2, . . . locations of the first recording layer 3 in which arerecorded first data relevant to the second data. In particular, thesecond data is recorded within a range D1 accessible for the objectivelens 15 of the optical pickup, adapted for reading out the first andsecond data of the first and second recording mediums 3, 6 of theoptical disc 1, on shifting the objective lens from the positions A1, A2in the first recording layer 3, in which are recorded first datarelevant to the second data, in a direction indicated by arrow X in FIG.6 perpendicular to the recording tracks formed in the first and secondrecording layers 3, 6. This range Di is a range that may be accessedwithin the field of view of the objective lens 15 without performingsled feed of the optical pickup in a direction perpendicular to therecording track, by a pickup feed unit, not shown, and is specifically arange of, for example, approximately 200 μm. More specifically, thefirst and second data are recorded so that the leading ends of the areasof recording of the first and second data in the first and secondrecording layers 3 and 6 will be within a range of approximately 200 μmfrom each other. For example, if the first and second data are recordedin the first and second recording layers 3, 6 in the standard format forthe Compact Disc (CD), and if the range D1 which permits accessing onshifting the objective lens 15 within its field of view, the recordingstart positions of data of the first and second data are set so as to bewithin 60 concentrically or spirally extending recording tracks in thefirst and second recording layers 3 and 6.

The state of recording the first and second data, relevant to eachother, in the first and second recording layers 3, 3 a, 3 b, 6, 6 a, 6b, is now explained. This recording is explained with reference to arecording device 21 shown in FIG. 1. Of course, the present inventioncan be applied to optical discs 1 a, 1 b shown in FIGS. 2 and 3.

The recording device 21 shown in FIG. 7 includes a first input terminal22, fed with the first audio signals corresponding to the first datarecorded on the first recording layer 3 of the optical disc 1, and asecond input terminal 122, fed with the second audio signalscorresponding to the second data recorded on the second recording layer6.

The first and second audio signals, fed to the first and second inputterminals 22, 122, are analog audio signals, relevant to each other, andwhich form multi-channel audio signals which may be synthesized toenable the aforementioned surround reproduction. That is, the analogaudio signals, fed to the focussing servo input terminal s 22, 122, areconverted into left and right front channel data Lf, Rf and left andright rear channel data Lb, Rb, making up relevant audio data of frontand rear four channels by signal processing, as later explained, andwhich are subjected to sampling at the sampling frequency of 44.1 kHzand 16 bit quantization. The front channel data Lf, Rf and the rearchannel data Lb, Rb may be said to be relevant data at the same timepoint on the time axis.

It may be seen from above that the first input terminal 22 is fed withfirst audio signals, corresponding to the left and right front channeldata Lf, Rf, whilst the second input terminal 122 is fed with the secondaudio signals corresponding to the left and right rear channel data Lb,Rb.

The first audio signals, fed to the first input terminal 22, areamplified by a first line amplifier 23, and thence sent to a first adder25 for addition of a dither as a small random noise from a dithergenerator 24. From the first audio signals, added to with the dither bythe first adder 25, only a band 20 kHz or less is taken out by a firstLPF 26, and thence routed to a first sampling circuit 27, which thenapplies sampling processing at a sampling frequency of 44.1 kHz to afiltered output from the first LPF 26. The sampling data from the firstsampling circuit 27 is converted by a first A/D converter 28 into 16-bitdigital audio data.

In similar manner, the second audio signals, fed to the second inputterminal 122, are amplified by a second line amplifier 123, and thencesent to a second adder 125 for addition of a dither as a small randomnoise from the1 dither generator 24. From the second audio signals,added to with the dither by the second adder 25, only a band 20 kHz orless is taken out by a second LPF 26, and thence routed to a secondsampling circuit 127, which then applies sampling processing at asampling frequency of 44.1 kHz to a filtered output from the second LPF126. The sampling data from the second sampling circuit 127 is convertedby a second A/D converter 128 into 16-bit digital audio data.

The first digital data, converted into 16-bit digital audio data derivedfrom the first audio signals output by the first A/D converter 28, arestored in a first buffer memory 29. The first audio data, read out fromthe first buffer memory 29, is routed to a first error correctionencoding circuit 30 where it is encoded by the combination ofcross-interleaving and four-order Reed-Solomon code employing analgorithm of CIRC (Cross Interleave Reed Solomon Code) used in a CD. Theencoded data from the first error correction encoding circuit 30 isEFMed (eight-to-fourteen modulated) by a first modulation circuit 31 andprocessed by a first recording processing circuit 32 so as to berecorded by the optical pickup on the first recording layer 3 of theoptical disc 1.

The second digital data, converted into 16-bit digital audio dataderived from the second audio signals output from the second A/Dconverter 128, is stored in a second buffer memory 129. The second audiodata, read out from the second buffer memory 129, is routed to a seconderror correction encoding circuit 130 where it is encoded by thecombination of cross-interleaving and four-order Reed-Solomon codeemploying an algorithm of CIRC (Cross Interleave Reed Solomon Code) usedin a CD. The encoded data from the second error correction encodingcircuit 130 is EFMed (eight-to-fourteen modulated) by a secondmodulation circuit 131 and processed by a second recording processingcircuit 132 so as to be recorded by the optical pickup on the secondrecording layer 6 of the optical disc 1.

The first digital data recorded on the first recording layer 3 and thesecond digital data recorded on the second recording layer 6 arerecorded with time axis coincidence relative to each other.

In a manner contrary to the above-described embodiment, the left andright front channel data Lf, Rf derived from the first audio signals maybe recorded in the second recording layer 6, with the left and rightrear channel data Lb, Rb derived from the second audio signals beingthen recorded on the first recording layer 3.

A reproducing apparatus for reproducing an optical disc 1, havingrecorded thereon the first and second data pertinent to the first andsecond recording layers 3, 6, respectively, is now explained.

Referring to FIG. 8, the reproducing device includes an optical pickup41 and a signal readout unit 42 for reading out first and second datarecorded in the first and second recording layers 3, 6 of the opticaldisc 1, a first buffer memory 43 for storing the first data recorded inthe first recording layer 3 and read out by the optical pickup 41, asecond buffer memory 44 for storing the second data recorded in thesecond recording layer 6, a buffer management unit 46 for supervisingand controlling the writing and readout on or from the first and secondbuffer memories 43, 44, a multiplexer 45 for adding or subtractingoutputs read out from the first and second buffer memories 43, 44, and aservo circuit 48 for focussing and tracking controlling the objectivelens of the objective lens of the optical pickup 41 to focus the lightbeam radiated from the optical pickup 41 or to cause the light beamrdiated from the optical pickup 41 to follow the target recording trackon the optical disc 1. This servo circuit 48 includes a switching unit49 for switching the focussing position of the light beam radiated fromthe optical pickup 41 in order to converge the light beam by anobjective lens of the optical pickup 41 to focus the light beam on thefirst or second recording layer 3, 6. For switching, that is shifting,the focussing position of the light beam radiated from the opticalpickup 41 between the first recording layer 3 and the second recordinglayer 6, the objective lens of the optical pickup 41 is moved along theoptical axis of the objective lens. The reproducing apparatus includes aspindle motor 50 for causing the rotation of the optical disc 1 e.g., ata CLV under control by the servo circuit 48.

The reproducing apparatus 40 includes a controller (CPU) 47 fordetermining, under instructions from a user, whether the audio datarecorded on the first and second recording layers 3, 6 of the opticaldisc 1 is to be reproduced, whether audio data recorded on the first andsecond recording layers 3, 6 of the optical disc 1 are synthesized andreproduced or whether an optical disc such as a conventional opticaldisc is to be reproduced, depending on the configuration of the loadeddisc, based on instructions from a user, and for controlling the servocircuit 48, switching unit 49, signal read-out unit 42 and the buffermanagement unit 46, based on the result of decision. To this controller47 is connected an operating unit provided with plural operatingswitches, not shown, for a user to input the aforementionedinstructions. In place of the aforementioned instructions from the user,control signals may also be input to the controller 47 from an externalequipment, such as a personal computer, not shown.

In this reproducing apparatus 40, the audio data read out from the firstand second recording layers 3, 6 are adapted for being stored in thebuffer memories 43, 44. Alternatively, these audio data may also bestored in a sole common buffer memory.

In this reproducing apparatus 40, the first and second digital data,read out by the optical pickup 41 from the first and/or second recordinglayers 3, 6, are routed to the signal read-out unit 42. Based on thecontrol signal from the servo circuit 48 or the switching unit 49, theoptical pickup 41 switches the focussing position of the light beam onthe first recording layer 3 or on the second recording layer 6 forcontrolling the light beam focussing state to follow surface shaking ofthe optical disc 1 and for controlling the light beam to follow therecording tracks of the first and second recording layers 3, 6.

The signal read-out unit 42 performs pre-set playback signal processing,such as RF processing, demodulation or error correction processing, onthe first and second digital data read out from first or secondrecording layer 3 or 6, as output signal from the optical pickup 41, toroute output data derived from the first digital data and output dataderived from the second digital data to the first buffer memory 43 andto the second buffer memory 44, respectively.

The first buffer memory 43 is a playback memory for first digital data,read out from the first recording layer 3, whilst the second buffermemory 44 is a playback memory for second digital data, read out fromthe second recording layer 6. The first buffer memory 43 or the secondbuffer memory 44 is controlled and supervised by the buffer managementunit 46 as to data writing from the signal read-out unit 42 or datareadout from the buffer memory 44.

Next, the operation of the reproducing apparatus 40 shown in FIG. 8 isexplained in detail.

If a playback mode selection button of an operating unit, not shown,provided on the reproduction apparatus 40 and which is connected to thecontroller 47, is acted on by the user, and the playback mode ofmultiplexing and reproducing the first and second data recorded on thefirst and second recording layers 3, 6, is selected, the data isreproduced by the following operations: If the playback mode ofmultiplexing and reproducing the data is selected, the controller (CPU)47 decides to multiplex and reproduce the first and second data read outfrom the first and second recording layers 3, 6 of the optical disc 1.If the multiplexing reproduction is selected, the optical pickup 41 iscontrolled by the servo circuit 48 or the switching unit 49 so that thefocussing point of the playback light beam will be switched to the firstrecording layer 3 or to the second recording layer 6 based on thecontrol signal supplied from the controller 47. The timing of switchingof the focussing point of the light beam to the first recording layer 3or to the second recording layer 6 is such that, if second data recordedon the second recording layer 6 is to be reproduced after reproducingthe first data recorded on the first recording layer 3, the focussingpoint of the light beam is shifted to a location temporally ahead of areplay end point of the first data of the first recording layer 3 tostart the reproduction of the second data, the second data is reproducedto a location temporally posterior to a replay end point of the audiodata of the first recording layer 3 and the focussing point of the lightbeam is shifted to a location on the first recording layer 3 next to thelast readout point to reproduce the first data.

That is, if, after reproducing the first data from a point P11 to apoint P12 on the first recording layer 3, the focussing point of thelight beam is to be shifted to the second recording layer 6, as shown inFIG. 9A, the second data is started to be reproduced from a point P21temporally retrograding from a replay end point P12 of the firstrecording layer 3. After reproducing the second data to a point P22temporally posterior from the replay end point P12 of the firstrecording layer 3, the focussing point of the light beam is shifted to apoint P12 on the first recording layer 3 to start reproducing the firstdata. Data reproduction of the first data as from the point P12 of thefirst recording layer 3 is continued up to a point P13 temporallyposterior to the replay end point P22 of the second recording layer 6.If the light beam focussing point is to be shifted to the secondrecording layer 6, the first data is reproduced at a temporally previousreplay end point P13 of the second recording layer 6 up to a point P23temporally posterior from the replay end point P13 of the firstrecording layer 3.

The first and second data, read out from the first recording layer 3 andthe second recording layer 6 at the replay timing shown in FIG. 9A, arerouted to the signal read-out unit 42 where replay signal processingoccurs in accordance with the aforementioned timing. When outputtingreadout signals read out from the first recording layer 3 or the secondrecording layer 6, the signal read-out unit 42 outputs identificationsignals, pre-recorded on the first recording layer 3 and the secondrecording layer 6 for indicating the recording layers 3, 6,respectively, to the controller 47. The controller 47 thendiscriminates, based on the furnished identification signals, whetherthe output data from the signal read-out unit 42 has been read out fromthe first recording layer 3 or from the second recording layer 6, andcontrols the data writing or readout timing to or from the first andsecond buffer memories 43, 44 through the buffer management unit 46.

The data writing timing to the first and second buffer memories 43, 44is the same as the replay timing shown in FIG. 9A or the readout timingin the signal read-out unit 42. On the other hand, the data readouttiming from the first and second buffer memories 43, 44 is such that,after a pre-set amount of data has been written in one of the first andsecond buffer memories 43, 44, the data readout is started from theother of the first and second buffer memories 43, 44. Theoretically, theoptical disc 1 is run in rotation at an rpm not less than double thestandard rpm to read out the first and second data from the firstrecording layer 3 and the second recording layer 6 of the optical disc1, at a speed not less than the standard speed, to write data in thefirst and second buffer memories 43, 44. The first and second data,recorded on the first and second recording layers 3, 6, are read outfrom the respective buffer memories 43, 44 and output at an outputterminal 51 after multiplexing by a multiplexer 45. For reading out thefirst recording layer 3 and the second recording layer 6 at a haploidspeed, that is at a standard speed prescribed in the reference standardmanual, data readout from the optical disc 1 needs to be performed at aspeed twice the aforementioned standard speed, if the switching time forreproduction-timing of the first and second recording layers 3, 6 isdiscounted. In actuality, the spindle motor 50 is desirably run inrotation at a quadrupled or higher speed to read out data from theoptical disc 1.

Meanwhile, the timing of switching the focussing position of the replaylight beam, radiated from the optical pickup 41, between the firstrecording layer 3 and the second recording layer 6, under control by thecontroller 47, may be such timing as is shown in FIG. 9B. If data isreproduced from the point P11 up to the point P12 on the first recordinglayer 3, and reproduction is to be shifted to the second recording layer6, the focussing point of the replay light beam reverts to a pointtemporally previous to the replay end point P12 on the first recordinglayer 3 to start reproduction of the second data of the second recordinglayer 6 as from the point P21. After reproducing up to a point P22 ofthe same timing on the time axis as the replay end point of the firstrecording layer 3, the focussing point of the replay light beam isshifted to the point P12 on the first recording layer 3 to startreproduction of the first data of the first recording layer 3 as fromthe point P12. The first data continues to be reproduced from the pointP12 of the first recording layer 3 up to the point P13 temporallyposterior to the replay end point P22 of the second recording layer 6.If reproduction is to be shifted to the second recording layer 6, thefocussing position of the replay light beam reverts to the replay endtime point P22 of the second recording layer 6 to reproduce the seconddata of the second recording layer 6 up to the point P23, which is thesame time point as the replay end time point P13 of the first recordinglayer 3.

The signal read from the first recording layer 3 and the secondrecording layer 6 in the replay timing shown in FIG. 9B are routed tothe signal read-out unit 42 where replay signal processing is carriedout in accordance with the aforementioned timing.

By reproducing the first and second data, relevant to each other,recorded on the first and second recording layers 3, 6 of the opticaldisc 1, by the reproducing apparatus 40, shown in FIG. 8, and bysynthesizing the reproduced data by the multiplexer 45, it is possibleto achieve stereo reproduction of four channels comprising left andright front channel data and left and right rear channel data Lb, Rb.

The first and second data, recorded on the first and second recordinglayers 3, 6 of the optical disc 1, and which are related to each otherto constitute sole unit recording data, are recorded in a trackingcontrol range within the field of view of the objective lens, withoutrelying upon the sled feed of the optical pickup 41 by a pickup feedunit, not shown, in a direction along the radius of the optical disc 1,that is in a direction perpendicular to the recording track. So, it ispossible to reduce the amount of movement of the optical pickup 41 in adirection perpendicular to the recording track to reproduce andsynthesize the first and second data sequentially smoothly.

If, in the reproducing apparatus 40, shown in FIG. 8, a playback modeselection button of an operating unit, not shown, provided in theapparatus 40, is acted on by the user, and the user's command is toreproduce only the first data recorded on the first recording layer 3 ofthe optical disc 1, the operating unit 47 decides reproduction only ofthe first data from the first recording layer 3. At this time, theoptical pickup 41 is controlled by the servo circuit 48 and theswitching unit 49 so that the light beam is focussed on the firstrecording layer 3 of the optical disc rotationally driven by the spindlemotor 50 to scan only the first recording layer 3. If the optical pickup41 is controlled to scan the first recording layer 3, the return lightbeam, reflected only from the first recording layer 3, is received by aphotodetector of the optical pickup 41, an output signal of which isrouted to the signal read-out unit 42 where signal processing isperformed on the audio data recorded on the first recording layer 3. Thefirst data recorded on the first recording layer 3 detected by thesignal read-out unit 42 is processed in a pre-set fashion and written inthe first buffer memory 43 at a pre-set timing under control by thebuffer management unit 46. The data is then read out from the firstbuffer memory 43 and output via multiplexer 45 at the output terminal51.

The first data, read out from the first recording layer 3, is convertedvia an error interpolator, an LPF and a D/A converter, all not shown,connected to the output terminal 51, into analog audio signals, whichare output.

If the replay mode selection button of an operating unit, not shown,provided in the reproducing apparatus 40, is acted on by the operator,and the replay mode of reproducing only the second data recorded on thesecond recording layer 6 of the optical disc 1 is selected, theprocessing similar to that in case of the selection of the reproducingmode of reproducing only the first recording layer 3 is performed toread out the second data recorded in the second recording layer 6, andthe data so read out is output as the reproduced second data at theoutput terminal 51. Alternatively, the second data may be converted intoand output as analog audio signals, as in the case of the aforementionedfirst data.

Meanwhile, if the optical disc 1 of the present invention is arranged asshown for example in FIG. 3, in which the second recording layer 6 ofthe focussing servo recording layers 3, 6, in which to record left andright front channel data Lf, Rf corresponding to the first audiosignals, is of a reflectance which permits reproduction by a reproducingapparatus capable of reproducing a routine CD, and recording thereon ismade in a format satisfying the CD format, the optical disc 1 b can bereproduced in the reproducing apparatus designed to reproduce theroutine CD. Four-channel stereo reproduction can be realized by using areproducing apparatus configured as shown in FIG. 8 for reproducing thefirst and second recording layers 3 b, 6 b and by synthesizing andreproducing left and right front channel data Lf, Rf and left and rightrear channel data Lb, Rb.

Of the four-channel audio data, recorded in the optical disc 1, left andright front channel data Lf, Rf are recorded as first data in the firstrecording layer 3, while left and right rear channel data Lb, Rb arerecorded as second data in the second recording layer 6. Alternatively,a variety of data relevant to one another to constitute sole unitrecording data may be recorded in the focussing servo recording layers3, 6.

If the audio data recorded on the optical disc 1 is multi-channel datacomprised of left and right front channel data Lf, Rf, input to the leftand right front speakers 61, 62, arranged on the front side of anacoustic space, rear channel data B input to a rear speaker 63 arrangedon the rear side and a high channel data H input to an upper speaker 64arranged above the listener's head, as shown in FIG. 10, it issufficient if the front channel data Lf, Rf are recorded as first datain the first recording layer 3 and the rear channel data B and the upperchannel data H are recorded as second data in the second recording layer6.

If the multi-channel data is recorded in a split fashion in the firstand second recording layers 3, 6 and only the first data recorded in thefirst recording layer 3 is reproduced, two-channel stereo reproductionby the left and right front speakers 61, 62 can be performed, whereas,if the first and second data recorded in the first and second recordinglayers 3, 6 are synthesized and reproduced, multi-channel stereoreproduction can be performed using the left and right front speakers61, 62, rear speaker 63 and the upper speaker 64.

On the other hand, if the audio data recorded on the optical disc 1 isthe multi-channel data made up of left and right front channel data Lf,Rf input to the left and right front speakers 71, 72 arranged forwardlyof an acoustic space, rear channel data Lb, Rb input to the left andright rear speakers 73, 74, arranged at back of the acoustic space, andthe upper channel data H input to the upper speaker 75, arrangedoverhead, as shown in FIG. 12, the front channel data Lf, Rf arerecorded as first data in the first recording layer 3, whilst the rearchannel data Lb, Rb and the upper channel data H are recorded as seconddata in the second recording layer 6, as shown in FIG. 13. At this time,the rear channel data Lb, Rb and the upper channel data H are recordedin upper 12 bits and in lower 4 bits of the quantized 16-bit second dataof each of the left and right channels recorded in the second recordinglayer 6, respectively.

Referring to FIG. 14, it is also possible to record 16-bit front channeldata Lf, Rf as first data in the first recording layer 3, and to recordthe rear channel data Lb, Rb, data of audio signals of the mid frequencyrange and data of the audio signals in the low frequency range, in upper10 bits, mid 5 bits and in the lower one bit of the quantized 16-bitsecond data of each of the left and right channels recorded in thesecond recording layer 6.

In recording the first and second data as shown in FIGS. 13 and 14, thefirst and second data are recorded in a range that can be accessed bymovement in the field of view of the objective lens of the opticalpickup 41.

By recording data relevant to one another to constitute a unit recordingdata in the first and second recording layers or in three or morerecording layers, in a split fashion, it is possible not only toincrease the recording capacity on a disc but also to reproduce theinformation of variable sorts.

The first and second data recorded in the first and second recordinglayers of the optical disc may constitute, in addition to theaforementioned multi-channel audio data, data relevant to one another ora sole recording data unit, as now explained.

For example, there are occasions where the first data is upper orderbits of the quantized data, with the second data then being lower orderbits of the quantized data, the first data is audio data, with thesecond data being text data relevant to this audio data, such as lyric,or image data, the first data is image data, with the second data thenbeing data relevant to the image data, such as title or synopsis data,and so on. In these cases, the audio data as the first data or the imagedata, reproduced alone, may be handled as meaningful data, whilst thesecond data, such as text or title data, may also be handled as sub-datarelevant to the first or main data. Of course, the combination of thefirst and second data may be other than that explained above only by wayof illustration.

If, in recording the first and second data, relevant to each other, inthe first and second recording layers of the optical disc, the first andsecond data are recorded with the same format, inclusive of therecording density, in the recording tracks formed at approximately equalpositions of the first and second recording layers, it is sufficient tocause the movement of the objective lens in a direction parallel to theoptical axis of the objective lens along the direction of thickness ofthe optical disc, that is in the focussing direction, when the first andsecond data recorded in the first and second recording layers are readout in a switching fashion by the sole optical pickup, thus assuringfacilitated control of the optical pickup.

In the above-described embodiment, the optical recording medium is anoptical disc, however, the optical recording medium may also be a cardtype recording medium, such as an optical card.

Industrial Applicability

According to the present invention, as described above, the second datarecorded in the second recording layer of first and second recordinglayers layered together is recorded in a location adjacent to a locationof the first recording layer where the first data relevant to the seconddata is recorded. So, the movement range of readout means, such asoptical pickup, for reading out the first and second data recorded indifferent recording layers can be diminished and hence the first andsecond data can be read out smoothly in a switching fashion to reducethe size of the buffer memory provided in the reproducing apparatus torealize saving in power consumption.

Moreover, since the relevant data can be recorded in plural recordinglayers, replay signals of variable configurations can be produced bysuitably synthesizing data read out from the respective recordinglayers.

1. A reproducing apparatus for an optical recording medium having afirst recording layer for recording first data and a second recordinglayer for recording second data, wherein said first and said secondrecording layers are positioned adjacent to one another and said seconddata is recorded at a location in said second recording layer inproximity to a location in said first recording layer where first datarelevant to said second recording layer is recorded, said reproducingapparatus comprising: readout means for reading said first data derivedfrom a selected audio program and second derived from the same selectedaudio program from said optical recording medium; reproducing means forgenerating replay signals based on said first and said second data readfrom said readout means; and control means for controlling said readoutmeans and said reproducing means, wherein said readout means includes anobjective lens for reading one of said first and said second data andsaid second data is recorded in a range accessible by said objectivelens by shifting a focus of said objective lens from a location of saidfirst recording layer where said first data relevant to said second datais recorded to said location of said second layer where said second datais recorded, wherein said control means controls to alternately readsaid first data recorded in said first recording layer and said seconddata recorded in said second recording layer, and wherein saidreproducing means includes a first buffer memory for holding said firstdata read and reproduced from said first recording layer by said readoutmeans; a second buffer memory for holding said second data read andreproduced from said second recording layer by said readout means; andsynthesis means for synthesizing said first data read from said firstbuffer memory and said second data read from said second buffer memory.2. The reproducing apparatus according to claim 1, wherein said controlmeans controls to synthesize said first and said second data read fromsaid readout means to output said replay signals.
 3. A reproducingapparatus for an optical recording medium having a first recording layerfor recording first data and a second recording layer for recordingsecond data constituting a single recording data unit, said first andsaid second recording layers being mounted adjacent to one another andsaid second data being recorded at a location in said second recordinglayer in proximity to a location in said first recording layer wherefirst data relevant to said second recording layer is recorded, saidreproducing apparatus comprising: readout means for reading said firstdata derived from a selected audio program and said second data derivedfrom the same selected audio program from said optical recording medium;reproducing means for generating replay signals based on said first andsaid second data read from said readout means; and control means forcontrolling said readout means and said reproducing means, wherein saidreadout means includes an objective lens and said second data isrecorded in a range accessible by said objective lens by shifting afocus of said objective lens from said location of said first recordinglayer where said first data relevant to said second data is recorded tosaid location of said second layer where said second data is recorded,and wherein said readout means includes a first buffer memory forholding said first data read by said readout means from said firstrecording layer and reproduced: a second buffer memory for holding saidsecond data read by said readout means from said second recording layerand reproduced; and a synthesis unit for synthesizing said first dataread from said first buffer memory and said second data read from saidsecond buffer memory.
 4. The reproducing apparatus according to claim 3,wherein said control means controls said reproducing means to synthesizesaid first and said second data read by said readout means to outputsaid replay signals.